1. Field of the Invention
The present invention relates to a piezoelectric thin film usable as an actuator in ink jet recording apparatuses and the like.
2. Background Art
Piezoelectric and ferroelectric thin films represented by lead zirconate titanate ("PZT") thin films can be prepared by sputtering, sol-gel processing, CVD, laser ablation or other processes.
In particular, according to the sol-gel process, the composition of the PZT film can be easily controlled. Further, the sol-gel process has an additional advantage that a thin film can be successfully formed by repeating the step of coating a sol composition and the step of presintering the coating. In addition, patterning by photoetching can be carried out during the preparation of a piezoelectric device by the sol-gel process so that the PZT film is easily formed into a piezoelectric device. An ink jet recording head using a piezoelectric thin film prepared by the sol-gel process has also been proposed (Japanese Patent Laid-Open No. 504740/1993). A film thickness of about 0.5 to 20 .mu.m is in general necessary for a piezoelectric device for an ink jet recording head. Further, in the piezoelectric device for the ink jet recording head, the piezoelectric strain constant is high. The growth of crystal grains by annealing at a temperature of 700.degree. C. or above may be necessary to preferably provide such a high piezoelectric strain constant.
However, an attempt to prepare a piezoelectric thin film having a certain film thickness, for example, a film thickness of not less than 1 .mu.m, by the sol-gel process has often cracks in the film during annealing step for the formation of a perovskite structure.
Further, a method in which comprises the steps of coating a sol composition, heating the coating at a high temperature to cause crystallization, and repeating the steps to increase the film thickness has been proposed (e.g., Philips J. Res. 47 (1993) 263-285). So far as the present inventors know, however, the piezoelectric thin film prepared by this method has an interface created by the lamination, i.e., a multilayer structure. The presence of the interface adversely affects piezoelectric properties and often makes it impossible to realize good patterning by etching in the preparation of a piezoelectric device with the thin film.
Therefore, a need still exists for a piezoelectric thin film having good properties and a method for producing the same has been desired in the art.